Satellite transponder technology?

[alexandicity]

Hi guys,

Not sure if this is the right forum to ask but I thought I'd ping nonetheless!

I am trying to look at the history of the broadcast satellite transponder. You know, the bent pipes in geostationary orbit that give us our TV and the like. Clearly, over the last 30 years, the amount of data they have handled has increased massively, with the proliferation of channels, the adoption of HD (and 3D?) and the provision of satellite broadband.

What I want to know is how is a transponder's capacity measured. I know that the number of transponders on a satellite is an important factor, which is why modern satellites have 10 times more that ones built 30 years ago. But is the number of transponders the only driver of capacity? Is a single transponder today basically equal in capacity to a transponder made 30 years ago? Could I drive an HD channel through an early INTELSAT?

 

[uhf-satcom.com]

Satellite tpx

Hi,

You asked, "What I want to know is how is a transponder's capacity measured."

Generally the bandwidth of the transponder is measured in MHz. Intelsat 1 / Early bird apparently had 2 transponders, each of 25MHz bandwidth and 6 watts of RF power, but the antennas were not despun, so it effectively radiated out most of its power into space! Compare that early satellite with say Intelsat 10-02 which has 70 X 36MHz wide C-Band transponders, and 32 X 36MHz wide Ku-band transponders, thats 3672MHz of total bandwidth, verses 50MHz total bandwidth of Intelsat 1. It would be possible to get an HD signal through a 25MHz transponder of Intelsat 1, but you would require significant uplink power, as well as very large downlink dishes, due to the low EIRP of the satellite.

Telstar-1 had a single 50MHz wide C-Band transponder running 2 whole Watts of RF power!!

Apparently the Intelsat 1 was reactivated for some anniversary - that would have been quite interesting to have a go at detecting signals from it.

regards,

Paul
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